SW6190901_Calcs (SCM)_20200215

LA ENGINEERING - SURVEYING - DESIGNING - DRAFTING
Larry King & Associates, R.L.S., P.A.
P. [phone] www.LKandA.com F. [phone]
Stormwater Wet Pond Design Criteria
Project Name: P19-014 Hoke Landing Phase 2
Outlet: 1
Calculate Runoff Coefficient
A= 6.68 acres
Ai= 5.24 acres
la= 0.78
Rv=0.05+0.9*la
Rv= 0.76
290,955 sf Watershed area
228,200 sf Impervious area
Impervious fraction
Runoff Coefficient
Calculate Runoff Volume Required to be Controlled
Rd= 1 in Design storm rainfall depth (typically 1" or 1.5")
V=3630*Rd*Rv*A
WQV= 18,327 cf Volume of runoff that must be
5.06 Ac in controlled for specified design storm
Calculate Required Pond Surface Area for Permanent Pool Elevation
SA/DA= 3.7 Based, 4 Avg. Perm. Pool Depth
*"See Table 10-1,10-2,10-3 for SAIDA
SA= 0.247 Ac
10,765 sf Required Surface Area @ Perm Pool
SC-3

Project Name:
Outlet:
Pond Storage=
Pond Depth(h)=
Drawdown Time=
Cid=
9=
The Orifice Equation
ENGINEERING. SURVEYING - DESIGNING - DRAFTING
Lany King & Associates, R.L.S., P.A.
P. [phone] www.LKandA.com F. [phone]
Drawdown Orifice Sizing Calculations
P19-014 Hoke Landing Phase 2
1
18,327 cf Water Quality Volume
0.3333 ft HO=H/3
2.5 days 2-5 days
0.6 Coefficient of Discharge (typical 0.6)
32.2 ft/sec^2 Gravity
Q= Cd A Sgrt(2 g h)
Rearrange to solve for A, the minimum orifice area needed to meet drawdown requirements
Q= 0.08 cfs Based on pond volume and desired drawdown time
A- 0.03052 sf 4.40 si
Number of Orifices= 1
Minimum diameter to meet area
d=
Use:
Check Outflow time
Q= Cd A Sgrt(2 g h)
Q=
Drawdown time=
2.37 inch diameter orifice
2 " diameter orifice 0.0218 sf
0.06 cfs
3.50 days OK
SC-5

ENGINEERING - SURVEYING - DESIGNING - DRAFTiNG
Larry King & Associates, R.L.S., P.A.
P. [phone] www.LKandA.com F. [phone]
Pond Volume Calculations
Project Name: 1319-014 Hoke Landing Phase 2
Outlet: 1
Permanent Pool Volume (Main+Forebay)
t-lev. Contour Accum.
Stage Diff Area Incr. Vol. Vol.
(ft) (ft) (Sf) (cf) (cf)
238
0.0
3,611
0
0
239
1.0
4,486
4,049
4,049
240
1.0
5,417
4,952
9,000
241
1.0
6,406
5,912
14,912
242
1.0
7,454
6,930
21,842
243
1.0
8,562
8,008
29.850
243.5
0.5
9,137
4,425
34,274
244
0.5
10,743
4,970
39,244
Forebay Only Volume
Stage
ev,
Diff
Contour
Area
Incr. Vol.
Accum.
Vol.
(ft)
(ft)
(SO
(cf)
(cf)
240
0.0
1031
0
0
241
1.0
1291
1.161
1,161
242
1.0
1580
1,436
2,597
243
1.0
1898
1,739
4.336
243.5
0.5
2067
991
5,327
244
0.5
2574
1,160
6,487
Temporary Pool Volume
Stage
ev.
Diff
uontour
Area
Incr. Vol.
Accum.
Vol.
(ft)
(ft)
(Sf)
(cf)
(cf)
244
0.0
10,742
0
0
244.5
0.5
12,320
5,766
5,766
245
0.5
13,130
6,363
12,128
18,899
245.5
0.5
13,953
6,771
Permanent Pool Volume (Main Only)
ev. Contour Accum.
Stage Diff Area Incr. Vol. Vol.
(ft) (ft) (Sf) (cf) (cf)
237
0.0
2380
0
0
238
1.0
3018
2,699
2,699
239
1.0
3687
3,353
6,052
240
1.0
4386
4,037
10,088
241
1.0
5115
4,751
14,839
242
1.0
5874
5,495
20,333
243
1.0
6664
6,269
26,602
243.5
0.5
7070
3,434
30.036
244
0.5
8169
3,810
33,845
Avg. Depth= 4.14 ft
Perm Pool Elev.
16.53%
18,327 cf
Perm Pool Elev.
Temp Pool Elev.
SC-7